1. Field of the Invention
The present invention relates to a light receiving and emitting integrated device, an optical pickup provided therewith, and an optical disk apparatus.
2. Description of the Related Art
The optical information recording/reproducing method that information is digitally recorded on an optical recording medium and reproduced from an optical recording medium using light has been widely used because the method has a large number of merits, for example, it is possible to perform recording/reproducing without contact, and the method is compatible with the respective forms of memories such as a playback-only type, a recordable type and a rewritable type.
As an optical pickup that is provided in an optical information recording and reproducing apparatus and that records information on an optical recording medium and/or reproduces information recorded on an optical recording medium using light, there are a so-called discrete package type using the combination of a light emitting element such as a laser diode (abbreviated to LD) and a light receiving element that are packaged separately, and a type using a light receiving and emitting integrated device such as a hologram laser in which a semiconductor chip as a light emitting element and a part of the optical components such as a light receiving element are integrated.
In both the types of optical pickups, in order to read an information signal of an optical recording medium or record an information signal on an optical recording medium, a focus servo signal and a track servo signal are necessary to condense light on a track of the optical recording medium and control its condensing state and its condensing position.
In general, an optical pickup of the discrete package type employs an astigmatic method for a focus servo signal, while an optical pickup of the type using the light receiving and emitting integrated device employs a knife edge method for a focus servo signal. Therefore, methods for detecting focus servo signals are different. Moreover, due to the difference in detecting methods, the optical pickup of the discrete package type and the optical pickup of the type using the light receiving and emitting integrated device have a difference in the division numbers of lights and operation equations that generate focus servo signals and track servo signals employed thereby.
FIG. 11 is a system view showing a configuration of a conventional optical pickup 1 of the discrete type in a simplified manner, and FIG. 12 is a plan view showing a configuration of a light receiving element 13 provided in the optical pickup 1 shown in FIG. 11. As an example of the optical pickup 1 of the discrete type, an apparatus that is compatible with two kinds of optical recording mediums using lights of different wavelengths for recording/reproducing of information, for example, a compact disk (abbreviated to CD) using an infrared light whose wavelength is 780 nm and a digital versatile disk (abbreviated to DVD) using a red light whose wavelength is 650 nm, will be shown.
The optical pickup 1 comprises a first semiconductor laser 2, a first diffraction grating 3, a second semiconductor laser 4, a second diffraction grating 5, a polarization beam splitter 6, a half mirror 7, a quarter-wave plate 8, a collimator lens 9, a lifting mirror 10, an objective lens 11, a coupling lens 12, and a light receiving element 13. The first semiconductor laser 2 emits the red light. The first diffraction grating 3 diffracts the light emitted from the first semiconductor laser 2. The second semiconductor laser 4 emits the infrared light. The second diffraction grating 5 diffracts the light emitted from the second semiconductor laser 2. The polarization beam splitter 6 transmits the light emitted from the first semiconductor laser 2 and reflects the light emitted from the second semiconductor laser 4. The half mirror 7 reflects the light from the polarization beam splitter 6. The quarter-wave plate 8 polarizes the light reflected by the half mirror 7. The collimator lens 9 substantially collimates the light passed through the quarter-wave plate 8. The lifting mirror 10 bends the light transmitted by the collimator lens 9 substantially at a right angle and guides to an optical recording medium 14. The objective lens 11 condenses the light reflected by the lifting mirror 10 to the optical recording medium 14. The coupling lens 12 condenses the light that is reflected by the optical recording medium 14, transmitted by the objective lens 11 again, reflected by the lifting mirror 10 and transmitted by the collimator lens 9, the quarter-wave plate 8 and the half mirror 7. The light receiving element 13 is irradiated with the light condensed by the coupling lens 12.
Although the optical pickup 1 of the discrete package type is provided with two semiconductor lasers, that is, the first and second semiconductor lasers 2, 4 that emit the lights of different wavelengths, respectively, the optical pickup 1 is provided with a single light receiving element 13 that receives a light reflected by the optical recording medium 14. The light receiving element 13 of this example comprises eight light receiving segments (A, B, C, D, E, F, G, H), four (A, B, C, D) of the light receiving segments are placed in the middle, and on both sides of the four light receiving segments (A, B, C, D), two groups of two light receiving segments (E, F), (G, H) are placed so as to be symmetrical with respect to the four light receiving segments (A, B, C, D).
For example, the light emitted from the first semiconductor laser 2 is diffracted into one main beam and two sub beams by the first diffraction grating 3. The main beam and the sub beams are condensed as three beam spots on a information recording surface of the optical recording medium 14, and the light receiving element 13 is irradiated with the three beams reflected by the optical recording medium 14 along the aforementioned light path. Hereinafter, irradiation of the light receiving element (the light receiving segments) with light will be referred to as incidence in some cases.
The main beam is incident on the four light receiving segments (A, B, C, D), and a reproduction signal of information recorded on the optical recording medium, a focus servo signal and a track servo signal are detected from the main beam. The two sub beams are incident on the two groups of two light receiving segments (E, F), (G, H), respectively, and the complementary signals of the track servo signal are detected from the sub beams.
FIGS. 13A to 13C are plan views showing states in which a main beam M and sub beams S1, S2 are incident on the light receiving element 13. In the optical pickup 1 of the discrete package type, a focus servo signal can be obtained by the astigmatic method. In the astigmatic method, beam spots M, S1, S2 form substantially circular shapes on the light receiving element 13 at the time of focus, and the beam spots M, S1, S2 form substantially oval shapes on the light receiving element 13 at the time of defocus.
When expressing signals detected from the respective light receiving segments (A, B, C, D, E, F, G, H) composing the light receiving element 13 by adding ‘S’ to each of the heads of the alphabets denoting the respective light receiving segments, the respective servo signals are generated by operation processing of equations (1) to (3) shown below.Focus servo signal FES=(SA+SC)−(SB+SD)  (1)Track servo signal DPP=(SA+SB)−(SC+SD)−k{(SE−SF)+(SG−SH)}  (2)Track servo signal DPD=(SA+SC)−(SB+SD)(Operation of phase difference)  (3)
Here, k is an amplification factor set as necessary (as well as in equations shown hereinafter), and there are two operation equations for obtaining track servo signals because either one is selected and used depending on the kind of an optical recording medium such as a DVD or a CD, and depending on the use such as reproducing or recording. As shown in FIGS. 13A to 13C and the operation equations shown above, in the optical pickup 1, the main beam M is incident on the four light receiving segments (A, B, C, D), and a focus servo signal is obtained with the signals (SA, SB, SC, SD) detected by the four light receiving segments (A, B, C, D), respectively, by the astigmatic method. Track servo signals are obtained with the signals (SA, SB, SC, SD) detected by the four light receiving segments (A, B, C, D) on which the main beam M is incident and the signals (SE, SF, SG, SH) detected by the two groups of two light receiving segments (E, F), (G, H) on which the two sub beams S1, S2 are incident, respectively.
In the optical pickup 1 of the discrete package type configured so as to be compatible with different kinds of optical recording mediums such as CD and DVD using lights of different wavelengths, respectively, for recording/reproducing information as described above, in general, the lights of different wavelengths are caused to be incident on the same light receiving segments in the one light receiving element 13, and therefore the optical pickup 1 is configured so that output signals of CD and DVD are outputted from the same output terminals, and provided with merely one system of output terminals.
FIG. 14 is a system view showing the configuration of a conventional optical pickup 20 of the type using a light receiving and emitting integrated device in a simplified manner, and FIG. 15 is a plan view showing the configuration of a light receiving element 26 provided in the optical pickup 20 shown in FIG. 14. The optical pickup 20 of the type using a light receiving and emitting integrated device has a configuration similar to that of the optical pickup 1 of the discrete package type, so that similar portions will be denoted by the same reference numerals, and the description thereof will be omitted.
The optical pickup 20 of the type using a light receiving and emitting integrated device is characterized in that a light receiving and emitting integrated device in which at least a light emitting element and a light receiving element are integrally packaged is provided therein. In the optical pickup 20 shown as an example here, the light receiving and emitting integrated device is a hologram laser, and a first light receiving and emitting integrated device 21 that emits a red light and receives a light reflected by an optical recording medium, and a second light receiving and emitting integrated device 22 that emits an infrared light and receives a light reflected by the optical recording medium, are provided.
The first light receiving and emitting integrated device 21 comprises a first semiconductor laser 23, a first diffraction grating 24, a first hologram element 25 and a first light receiving element 26. The first semiconductor laser 23 emits a red light. The first diffraction grating 24 diffracts the light emitted from the first semiconductor laser 23. The first hologram element 25 divides and diffracts the light reflected by the optical recording medium 14 and causes to be incident on a first light receiving element 26. The first light receiving element 26 receives and detects light divided by the first hologram element 25. The second light receiving and emitting integrated device 22 is similar to the first light receiving and emitting integrated device 21 except that a semiconductor laser is a second semiconductor laser 27 that emits an infrared light, and comprises a second diffraction grating 28, a second hologram element 29, and a second light receiving element 30.
In the optical pickup 20 of the type using the light receiving and emitting integrated device, the light emitted from the first semiconductor laser 23 of the first light receiving and emitting integrated device 21 is received and detected by the first light receiving element 26 that is provided in the first light receiving and emitting integrated device 21 as well. The light emitted from the second semiconductor laser 27 of the second light receiving and emitting integrated device 22 is received and detected by the second light receiving element 30 that is provided in the second light receiving and emitting integrated device 22 as well.
The first and second light receiving elements 26, 30 are configured in the same manner, and comprise one group of two light receiving segments (A, B), and two groups of three light receiving segments (G, C, E), (F, D, H) which are placed symmetrically with respect to the two light receiving segments (A, B), respectively.
FIGS. 16A and 16B are views each showing a state in which a light reflected by the optical recording medium 14 is divided with the first hologram element 25 and caused to be incident on the first light receiving element 26, and FIGS. 17A to 17C are views showing states of light caused to be incident on the first light receiving element 26 at the time of focus and at the time of defocus. Since the first and second light receiving and emitting integrated devices 21, 22 perform the same light receiving operation, the first light receiving and emitting integrated device 21 will be described as a representative example. The first hologram element 25 is a light dividing element that has three divided regions, that is, first to third regions 25a, 25b, 25c and that divides light. The first hologram element 25 has a plane shape formed into a circle, which is firstly divided into two regions of the third region 25c and the remaining region by a first dividing line 31 passing through the center of the circle, and the remaining region of which is subsequently divided to the first and second regions 25a, 25b by a second dividing line 32 so as to intersect the first dividing line 31 at right angles, whereby it is formed so as to have three regions, that is, the first to third regions 25a, 25b, 25c. The first hologram element 25 is capable of diffracting light entering each of the three regions at each of the regions to divide the light.
The fact that the light emitted from the first semiconductor laser 23 is diffracted into one main beam and two sub beams by the first diffraction grating 24, and the main beam and the sub beams are reflected by the optical recording medium 14, is the same as in the optical pickup 1 of the discrete package type. The main beam M and the sub beams S1, S2 are further divided into three, respectively, by the first hologram element 25 divided into three regions, and caused to be incident on the first light receiving element 26.
FIG. 16A shows a state in which the main beam M is divided into three by the first hologram element 25 and caused to be incident on the first light receiving element 26, and FIG. 16B shows a state in which the sub beams S1, S2 are divided into three, respectively, by the first hologram element 25 and caused to be incident on the first light receiving element 26. The main beam M is divided into three by the first hologram element 25, and the three lights are caused to be incident on the two light receiving segments (A, B), the light receiving segment (C) of the three light receiving segments on one side, and the light receiving segment (D) of the three light receiving segments on the other side, respectively.
Further, the sub beams S1, S2 are divided into three by the first hologram element 25, respectively, and the sub beams S1, S2 diffracted by the first region 25a are caused to be incident on the light receiving segments (E, G) of the three light receiving segments on one side, and the sub beams S1, S2 diffracted by the second region 25b are caused to be incident on the light receiving segments (F, H) of the three light receiving segments on the other side. The sub beams S1, S2 diffracted by the third region 25c are caused to be incident between the two light receiving segments (A, B) and the three light receiving segments (G, C, E) on one side and between the two light receiving segments (A, B) and the three light receiving segments (F, D, H) on the other side, respectively.
In the optical pickup 20 of the type using a light receiving and emitting integrated device, a focus servo signal is obtained by the knife edge method. In the knife edge method, the beam spots M, S1, S2 form substantially circular shapes on the first light receiving element 26 at the time of focus, and the beam spots M, S1, S2 form shapes dependent on the respective regions of the first hologram element 25 on the light receiving element 26 at the time of defocus.
When expressing signals detected from the respective light receiving segments (A, B, C, D, E, F, G, H) composing the first light receiving element 26 by adding ‘S’ to each of the heads of the alphabets denoting the respective light receiving segments, the respective servo signals are generated by operation processing of equations (4) to (6) shown below.Focus servo signal FES=(SA−SB)  (4)Track servo signal DPP=(SC−SD)−k{(SE−SF)+(SG−SH)}  (5)Track servo signal DPD=(SC−SD)(Operation of phase difference)  (6)
As shown in FIGS. 16A and 16B and the operation equations shown above, in the optical pickup 20, a focus servo signal is obtained from signals (SA, SB) detected by the light receiving segments (A, B) by dividing the main beam M into three by the first hologram element 25 and causing one of the lights to be incident on and condensing so as to extend over the two light receiving segments (A, B). Track servo signals are obtained from signals (SC, SD) that the remaining two of the divisions of the main beam M divided into three by the first hologram element 25 are detected by the light receiving segments (C), (D) of the respective groups of three light receiving segments, and from signals (SE, SG, SF, SH) detected by the light receiving segments (E, G), (F, H) of the respective groups of three light receiving segments, of the sub beam S1, S2 divided into three by the first hologram element 25.
The optical pickup 20 of the type using a light receiving and emitting integrated device as described above is provided with the second light receiving and emitting integrated device 22 for recording/reproducing on/from CD and the first light receiving and emitting integrated device 21 for recording/reproducing on/from DVD, provided with the first and second light receiving elements 26, 30 individually in the light receiving and emitting integrated devices 21, 22, configured so that the output signal of CD and the output signal of DVD are outputted from output terminals connected to the respective light receiving elements, and provided with two systems of output terminals.
FIGS. 18A and 18B are views each showing connection of ICs provided in a conventional optical disk apparatus. FIG. 18A shows an optical disk apparatus 101 provided with the optical pickup 1 of the discrete package type, and FIG. 18B shows an optical disk apparatus 111 provided with the optical pickup 20 of the light receiving and emitting integrated device type.
The optical disk apparatus 101 provided with the optical pickup 1 of the discrete package type comprises the optical pickup 1, and a control circuit board portion 102. The control circuit board portion 102 includes a front-end IC 103 for an optical pickup of the discrete package type, and an IC 104 for system control.
An IC installed for connection with the optical pickup 1 of the discrete package type in the optical disk apparatus 101 is the front-end IC 103 for an optical pickup of the discrete package type that has eight terminals (A to H) corresponding, respectively, to eight output terminals disposed for the eight light receiving segments of the light receiving element 13 provided in the optical pickup 1. Since the front-end IC 103 for the optical pickup of the discrete package type has merely one system of connection terminals so as to correspond to the one system of output terminals provided in the optical pickup 1, a small-size one is used.
On the other hand, in the optical disk apparatus 111 provided with the optical pickup 20 of the light receiving and emitting integrated device type, the optical pickup 20 of the light receiving and emitting integrated device type has two systems of output terminals, that is, first-system output terminals (A to H) and second-system output terminals (A′ to H′), and therefore, as an IC installed for connection with the optical pickup 20, a front-end IC 113 for both the optical pickup of the discrete package type and the optical pickup of the light receiving and emitting integrated type is used. The front-end IC 113 for both the optical pickup of the discrete package type and the optical pickup of the light receiving and emitting integrated type disposed to the control circuit board portion 112 has two systems of connection terminals so as to correspond to the two systems of output terminals of the optical pickup 20, and therefore, it can be used for both the optical pickup of the discrete package type and the optical pickup of the light receiving and emitting integrated type, but it is large in size as compared with the aforementioned front-end IC 103 for the optical pickup of the discrete package type.
The IC installed in the optical disk apparatus generates a focus servo signal and a track servo signal in accordance with outputs from an optical pickup, but when the types of optical pickups are different as mentioned before, the methods for detecting focus servo signals, operation equations generating focus servo signals and track servo signals, the numbers of output terminals of detection signals, and so on are different, with the result that there arises a problem that, depending on what type of optical pickup is installed, an operation needs to be differentiated and the number of input terminals must be changed.
In order to deal with such a problem, it is desirable that an IC installed in an optical disk apparatus be configured so as to be compatible with both the discrete package type and the type using a light receiving and emitting integrated device as shown in FIG. 18B, but the number of circuits and terminals increases, and the IC becomes large in size against miniaturization, so that there are still many cases in which an IC that needs to be provided with only one input terminal and is compatible with only an optical pickup of the discrete package type is used.
A hologram laser as one of the light receiving and emitting integrated devices is highly reliable, and the knife edge method used for detection of the focus servo signal in the hologram laser has such a merit that noise of a track cross signal is hard to be superimposed on the focus servo signal, but an optical pickup using this device cannot be connected to an IC that is compatible with only an optical pickup of the discrete package type, with the result that there arises a problem that the combination with an IC is limited and design freedom is low.
Conventionally, a large number of techniques of branching or dividing light emitted from a light source and/or light emitted from a light source and reflected by an optical recording medium, and devising various methods for branching or dividing, thereby increasing the quality of a focus servo signal, a track servo signal and a reproduction signal and simplifying assembly and adjustment, have been proposed.
For example, some techniques have been proposed. In one technique, referring to Japanese Examined Patent Publication JP-B2 6-90798 (1994), a light path divider is disposed that divides a reflection light from an optical recording medium to four regions symmetrical with respect to two axes intersecting at right angles. The light path divider is configured so that the regions of one pair of the four regions forming two pairs in the light path divider come in contact with each other on a finite line segment and the regions of the other pair are isolated from each other by the one pair of regions. By detecting light divided with the light path divider with a six-division-type photodetector, stable detection of a track error and stable detection of a focus error in which wraparound of a track error is reduced to the utmost can be realized. In another technique, referring to Japanese Examined Patent Publication JP-B2 6-77335 (1994), a light receiving element is divided into four light receiving regions as well as a second diffraction element guiding a light reflected by an optical recording medium to the light receiving element is divided into three light entering regions. A zeroth-order diffraction light and ± first-order diffraction lights are caused to enter the specified light entering regions of the second diffraction grating, and lights diffracted by the second diffraction element are condensed to a specific light receiving region of the light receiving element, thereby facilitating adjustment of focus offset.
Although a lot of techniques of branching and/or dividing a light by devising an optical member as in JP-B2 6-90798, JP-B2 6-77335 and so on are disclosed, no attempt to make it possible to use an optical pickup of the type using a light receiving and emitting integrated device with an IC that is compatible with an optical pickup of the discrete package type is disclosed or suggested at all.